Membrane electrode assembly and method for hydrogen evolution by electrolysis

ABSTRACT

A membrane electrode assembly includes an anode having a first catalyst layer on a first gas-liquid diffusion layer, a cathode having a second catalyst layer on a second gas-liquid diffusion layer, and an anionic exchange membrane between the first catalyst layer of the anode and the second catalyst layer of the cathode. The first catalyst layer has a chemical structure of M′ a M″ b N 2  or M′ c M″ d C e , wherein M′ is Ni, Co, Fe, Mn, Cr, V, Ti, Cu, or Zn, M″ is Nb, Ta, or a combination thereof, 0.7≤a≤1.7, 0.3≤b≤1.3, a+b=2, 0.24≤c≤1.7, 0.3≤d≤1.76, and 0.38≤e≤3.61, wherein M′ a M″ b N 2  is a cubic crystal system and M′ c M″ d  C e  is a cubic crystal system or amorphous.

TECHNICAL FIELD

The technical field relates to membrane electrode assembly, and in particular it relates to method for hydrogen evolution by electrolysis with the membrane electrode assembly.

BACKGROUND

Seeking alternative energy is imperative now due to energy shortages, and hydrogen energy is the best choice. Hydrogen gas serving as fuel meets the requirements of environment protection, and electrolysis of water is the easiest way to generating hydrogen and oxygen. Although electrolyzing water to generate hydrogen has many advantages, it still has a fatal flaw of consuming a lot of energy and resulting in an overly high cost. The overly high energy consumption in the electrolysis of water is related to an overly high over potential, and the over potential is related to electrodes, electrolyte, and product of the electrochemical reaction. The electrodes are critical to enhance the electrolysis performance of water. Lowering the activity energy and increasing the reaction interface are critical factors of the electrolysis performance of water. The activity energy can be lowered by the catalyst influence on the electrode surface, which is determined by the inherent catalytic properties of the electrode material. Although noble metal IrO₂ is one of the most catalytic electrode materials, it is expensive. As such, IrO₂ must be replaced with other materials for lowering the cost.

Accordingly, a novel catalyst for further enhancing activities of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) for simultaneously achieving the catalyst activity and lowering the cost is called for.

SUMMARY

One embodiment of the disclosure provides a membrane electrode assembly, including: an anode having a first catalyst layer on a first gas-liquid diffusion layer; a cathode having a second catalyst layer on a second gas-liquid diffusion layer; and an anionic exchange membrane between the first catalyst layer of the anode and the second catalyst layer of the cathode, wherein the first catalyst layer has a chemical structure of M′_(a)M″_(b)N₂ or M′_(c)M″_(d)C_(e), wherein M′ is Ni, Co, Fe, Mn, Cr, V, Ti, Cu, or Zn, M″ is Nb, Ta, or a combination thereof, 0.7≤a≤1.7, 0.3≤b≤1.3, a+b=2, 0.24≤c≤1.7, 0.3≤d≤1.76, and 0.38≤e≤3.61, wherein M′_(a)M″_(b)N₂ is a cubic crystal system and M′_(c)M″_(d)C_(e) is a cubic crystal system or amorphous.

In some embodiments, the membrane electrode assembly is dipped in an alkaline aqueous solution.

In some embodiments, the first layer has a chemical structure of Ni_(a)Nb_(b)N₂, 0.7≤a≤1.51, and 0.49≤b≤1.30.

In some embodiments, the first layer has a chemical structure of Ni_(c)Nb_(d)C_(e), 0.90≤c≤1.47, 0.53≤d≤1.10, and 0.9≤e≤1.9.

In some embodiments, the first layer has a chemical structure of Ni_(c)Nb_(a)C_(e), 0.74≤c≤163, 0.37≤d≤1.26, and 0.38≤e≤1.30.

In some embodiments, the first layer has a chemical structure of Co_(c)Nb_(d)C_(e), 0.24≤c≤1.39, 0.61≤d≤1.76, and 0.63≤e≤3.61.

In some embodiments, the second catalyst layer has a chemical structure of M_(x)Ru_(y)N₂ or M_(x)Ru_(y), wherein M is Ni, Co, Fe, Mn, Cr, V, Ti, Cu, or Zn, 0<x<1.3, 0.7<y<2, x+y=2, M_(x)Ru_(y)N₂ is a cubic crystal system or amorphous, and M_(x)Ru_(y) is a cubic crystal system.

In some embodiments, each of the first gas-liquid diffusion layer and the second gas-liquid diffusion layer comprises a porous conductive layer.

In some embodiments, the first gas-liquid diffusion layer is a metal mesh, and the second gas-liquid diffusion layer is another metal mesh or a carbon paper.

In some embodiments, the first gas-liquid diffusion layer has a pore size of 40 micrometers to 150 micrometers, and the second gas-liquid diffusion layer has a pore size of 0.5 micrometers to 5 micrometers.

One embodiment of the disclosure provides a method for hydrogen evolution by electrolysis, including: dipping a membrane electrode assembly in an alkaline aqueous solution, wherein the membrane electrode assembly includes: an anode having a first catalyst layer on a first gas-liquid diffusion layer; a cathode having a second catalyst layer on a second gas-liquid diffusion layer; and an anionic exchange membrane between the first catalyst layer of the anode and the second catalyst layer of the cathode, wherein the first catalyst layer has a chemical structure of M′_(a)M″_(b)N₂ or M′_(c)M″_(d)C_(e), wherein M′ is Ni, Co, Fe, Mn, Cr, V, Ti, Cu, or Zn, M″ is Nb, Ta, or a combination thereof, 0.7≤a≤1.7, 0.3≤b≤1.3, a+b=2, 0.24≤c≤1.7, 0.3≤d≤1.76 and 0.38≤e≤3.61, wherein M′_(a)M″_(b)N₂ is a cubic crystal system and M′_(c)M″_(d)C_(e), is a cubic crystal system or amorphous; and applying a potential to the anode and the cathode to electrolyze the alkaline aqueous solution for generating hydrogen by the cathode and generating oxygen by the anode.

In some embodiments, the second catalyst layer has a chemical structure of M_(x)Ru_(y)N₂ or M_(x)Ru_(y), wherein M is Ni, Co, Fe, Mn, Cr, V, Ti, Cu, or Zn, 0<x<1.3, 0.7<y<2, x+y=2, M_(x)Ru_(y)N₂ is a cubic crystal system or amorphous, and M_(x)Ru_(y) is a cubic crystal system.

In some embodiments, each of the first gas-liquid diffusion layer and the second gas-liquid diffusion layer respectively comprises a porous conductive layer.

In some embodiments, the first gas-liquid diffusion layer is a metal mesh, and the second gas-liquid diffusion layer is another metal mesh or carbon paper.

In some embodiments, the first gas-liquid diffusion layer has a pore size of 40 micrometers to 150 micrometers, and the second gas-liquid diffusion layer has a pore size of 0.5 micrometers to 5 micrometers.

A detailed description is given in the following embodiments with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:

FIG. 1 shows a membrane electrode assembly in one embodiment.

FIG. 2 shows OER curves of Ru catalyst and Ni_(x)Ru_(y) catalysts in one embodiment.

FIG. 3 shows OER curves of Ru₂N₂ catalyst and Ni_(x)Ru_(y)N₂ catalysts in one embodiment.

FIG. 4 shows HER curves of Ru catalyst and Ni_(x)Ru_(y) catalysts in one embodiment.

FIG. 5 shows HER curves of Ru catalysts and Ni_(x)Ru_(y)N₂ catalysts in one embodiment.

FIG. 6 shows OER curves of Ni₂N₂ catalyst and Mn_(x)Ru_(y)N₂ catalysts in one embodiment.

FIG. 7 shows HER curves of Ni₂N₂ catalyst and Mn_(x)Ru_(y)N₂ catalysts in one embodiment.

FIG. 8 shows OER curves of Ni_(a)Nb_(b)N₂ catalysts in one embodiment.

FIG. 9 shows OER curves of Ni_(c)Nb_(d)C_(e) and Nb_(0.6556)C_(1.3444) catalysts in one embodiment.

FIG. 10 shows OER curves of Ni_(c)Nb_(d)C_(e) and Nb_(0.6556)C_(1.3444) catalysts in one embodiment.

FIG. 11 shows OER curves of Co_(c)Nb_(d)C_(e) and Nb_(0.6556)C_(1.3444) catalysts in one embodiment.

FIG. 12 shows OER curves of Co_(c)Nb_(d)C_(e) and Nb_(0.6556)C_(1.3444) catalysts in one embodiment.

FIG. 13 shows OER curves of Co_(c)Nb_(d)C_(e) and Nb_(0.6556)C_(1.3444) catalysts in one embodiment.

FIG. 14 shows OER curves of Co_(c)Nb_(d)C_(e) and Nb_(0.6556)C_(1.3444) catalysts in one embodiment.

FIG. 15 shows OER curves of Co_(c)Nb_(d)C_(e) and Nb_(0.6556)C_(1.3444) catalysts in one embodiment.

FIGS. 16 to 19 show curves of current versus voltage of membrane electrode assemblies in embodiments.

FIG. 20 shows the current diagram of a membrane electrode assembly after long-span use in one embodiment.

DETAILED DESCRIPTION

In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawing.

One embodiment of the disclosure provides a catalyst material with a chemical structure of M′_(a)M″_(b)N₂, wherein M′ is Ni, Co, Fe, Mn, Cr, V, Ti, Cu, or Zn, M″ is Nb, Ta, or a combination thereof, 0.7≤a≤1.7, 0.3≤b≤1.3, and a+b=2, wherein the catalyst material is cubic a crystal system. In one embodiment, M′ is Ni, M″ is Nb, 0.7≤a≤1.51, and 0.49≤b≤1.30. If a is too low (e.g. b is too high), the activity of the catalyst will be poor. If a is too high (e.g. b is too low), the activity and the stability of the catalyst will be poor.

One embodiment of the disclosure provides a catalyst material of M′_(c)M″_(d)C_(e), wherein M′ is Ni, Co, Fe, Mn, Cr, V, Ti, Cu, or Zn, M″ is Nb, Ta, or a combination thereof, 0.24≤c≤1.7, 0.3≤d≤1.76, and 0.38≤e≤3.61≤, wherein M′_(c)M″_(d)C_(e) is a cubic crystal system or amorphous. In one embodiment, M′ is Ni and M″ is Nb, 0.90≤c≤1.47, 0.53≤d≤1.10, and 0.9≤e≤1.9. In one embodiment, M′ is Ni and M″ is Nb, 0.74≤c≤1.63, 0.37≤d≤1.26, and 0.38≤e≤1.30. In one embodiment, M′ is Co and M″ is Nb, 0.24≤c≤1.39, 0.61≤d≤1.76, and 0.63≤e≤3.61. If c is too low (e.g. d is too high), the activity of the catalyst will be poor. If c is too high (e.g. d is too low), the activity and the stability of the catalyst will be poor. If e is too low, the activity of the catalyst is poor. If e is too high, the activity and the stability of the catalyst will be poor.

One embodiment of the disclosure provides a method of forming the catalyst material, including putting an M′ target and an M″ target in a nitrogen-containing atmosphere, wherein M′ is Ni, Co, Fe, Mn, Cr, V, Ti, Cu, or Zn, and M″ is Nb, Ta, or a combination thereof. Respectively providing powers to the M′ target and the M″ target, and providing ions to bombard the M′ target and the M″ target for sputtering depositing M′_(a)M″_(b)N₂ on the substrate, wherein 0.7≤a≤1.7, 0.3≤b≤1.3, a+b=2, and M′_(a)M″_(b)N₂ is a cubic crystal system. In one embodiment, the nitrogen-containing atmosphere has a pressure of 1 mTorr to 30 mTorr. If the pressure of the nitrogen-containing atmosphere is too low or too high, the nitridation cannot be efficiently performed. In one embodiment, the nitrogen-containing atmosphere includes carrier gas such as helium, argon, or another suitable inert gas. The nitrogen and the carrier gas have a partial pressure ratio of 0.1 to 10. If the partial pressure ratio of the nitrogen is too low or too high, the nitridation cannot be efficiently performed. The method respectively provides powers to the M′ target and the M″ target. For example, the power applied to the M′ target is 10 W to 200 W. If the power applied to the M′ target is too low, the M′ ratio in the catalyst material will be too low. If the power applied to the M′ target is too high, the M′ ratio in the catalyst material will be too high. On the other hand, the power applied to the M″ target is 10 W to 200 W. If the power applied to the M″ target is too low, the M″ ratio in the catalyst material will be too low. If the power applied to the M″ target is too high, the M″ ratio in the catalyst material will be too high. The power can be direct current power of RF power.

The method also provides ions to bombard the M′ target and the M″ target for sputtering depositing M′_(a)M″_(b)N₂ on the substrate. For example, nitrogen gas and the carrier gas can be excited by plasma to form ions, and the targets are bombarded by the ions. In one embodiment, the substrate includes a porous conductive layer, such as porous metal mesh (e.g. stainless steel mesh, Ti mesh, Ni mesh, Ni alloy mesh, niobium alloy mesh, copper mesh, or aluminum mesh). The pore size of the porous conductive layer is determined by the application of M′_(a)M″_(b)N₂. For example, if the porous conductive layer with M′_(a)M″_(b)N₂ thereon serves as the anode in OER to electrolyze an alkaline aqueous solution, the porous conductive layer will have a pore size of 40 micrometers to 150 micrometers.

One embodiment of the disclosure provides a method of forming the catalyst material, including putting an M′ target, an M″ target, and a carbon target in an atmosphere of carrier gas, wherein M′ is Ni, Co, Fe, Mn, Cr, V, Ti, Cu, or Zn, and M″ is Nb, Ta, or a combination thereof. Respectively providing powers to the M′ target, the M″ target, and the carbon target, and providing ions to bombard the M′ target, the M″ target, and the carbon target for sputtering depositing M′_(c)M″_(d)C_(e) on the substrate, wherein 0.24≤c≤1.7, 03≤d≤1.76, 0.38≤e≤3.61, and M′_(c)M″_(d)C_(e) is a cubic crystal system or amorphous. In one embodiment, the atmosphere of carrier gas has a pressure of 1 mTorr to 30 mTorr. If the pressure of the atmosphere of carrier gas is too low or too high, the effective crystal cannot be formed. In one embodiment, the carrier gas can be helium, argon, another suitable inert gas, or a combination thereof. The method respectively provides powers to the M′ target, the M″ target, and the carbon target. For example, the power applied to the M′ target is 10 W to 200 W. If the power applied to the M′ target is too low, the M′ ratio in the catalyst material will be too low. If the power applied to the M′ target is too high, the M′ ratio in the catalyst material will be too high. The power applied to the M″ target is 10 W to 200 W. If the power applied to the M″ target is too low, the M″ ratio in the catalyst material will be too low. If the power applied to the M″ target is too high, the M″ ratio in the catalyst material will be too high. On the other hand, the power applied to the carbon target is 10 W to 200 W. If the power applied to the carbon target is too low, the carbon ratio in the catalyst material will be too low. If the power applied to the carbon target is too high, the carbon ratio in the catalyst material will be too high. The power can be direct current power of RF power.

The method also provides ions to bombard the M′ target, the M″ target, and the carbon target, to sputtering deposit M′_(c)M″_(d)C_(e) on the substrate. For example, the carrier gas can be excited by plasma to form ions, and the targets are bombarded by the ions. In one embodiment, the substrate includes a porous conductive layer, such as porous metal mesh (e.g. stainless steel mesh, Ti mesh, Ni mesh, Ni alloy mesh, niobium alloy mesh, copper mesh, or aluminum mesh). The pore size of the porous conductive layer is determined by the application of M′_(c)M″_(d)C_(e). For example, if the porous conductive layer with M′_(c)M″_(d)C_(e) thereon serves as the anode in OER to electrolyze an alkaline aqueous solution, the porous conductive layer will have a pore size of 40 micrometers to 150 micrometers.

In one embodiment, the catalyst material can be used as a membrane electrode assembly for generating hydrogen by electrolysis. As shown in FIG. 1, the membrane electrode assembly 100 includes an anode 11, a cathode 15, and an anionic exchange film 13 disposed between the anode 11 and the cathode 15. The anode 11 includes a catalyst layer 11B on the gas-liquid diffusion layer 11A, and the cathode 15 includes a catalyst layer 15B on the gas-liquid diffusion layer 15A. In addition, the anionic exchange film 13 is interposed between the catalyst layer 11B of the anode 11 and catalyst layer 15B of the cathode 15. The catalyst layer 11B has a chemical structure of M′_(a)M″_(b)N₂ or M′_(c)M″_(d)C_(e), and the definitions of M′, M″, a, b, c, d, and e are similar to those described above and not repeated here.

In one embodiment, the anionic exchange film 13 can be a halogen ion-containing imidazole polymer or other suitable materials. For example, the anionic exchange film can be FAS (commercially available from Fumatech) or X37-50 (commercially available from Dioxide materials). Because the membrane electrode assembly 100 is used to generate hydrogen by electrolyzing alkaline aqueous solution, the anionic exchange film 13 rather than other ionic exchange film is adopted.

In one embodiment, each of the gas-liquid diffusion layer 11A and the gas-liquid diffusion layer 15A respectively includes porous conductive layer. For example, the gas-liquid diffusion layer 11A can be a porous metal mesh (e.g. stainless steel mesh, Ti mesh, Ni mesh, Ni alloy mesh, niobium alloy mesh, copper mesh, or aluminum mesh). On the other hand, the gas-liquid diffusion layer 15A can be a porous metal mesh (e.g. stainless steel mesh, Ti mesh, Ni mesh, Ni alloy mesh, niobium alloy mesh, copper mesh, or aluminum mesh) or a porous carbon material (e.g. carbon paper or carbon cloth). In one embodiment, the gas-liquid diffusion layer 11A has a pore size of 40 micrometers to 150 micrometers. If the pore size of the gas-liquid diffusion layer 11A is too small, the mass transfer resistance will be increased. If the pore size of the gas-liquid diffusion layer 11A is too large, the active area will be lost. In one embodiment, the gas-liquid diffusion layer 15A has a pore size of 0.5 micrometers to 5 micrometers. If the pore size of the gas-liquid diffusion layer 15A is too small, the mass transfer resistance will be increased. If the pore size of the gas-liquid diffusion layer 15A is too large, the active area will be lost.

In other embodiments, the gas-liquid diffusion layer 11A of the anode 11 and the gas-liquid diffusion layer 15A of the cathode 15 have different pore sizes and/or different compositions if necessary. On the other hand, the elements or element ratios of the catalyst layer 11B of the anode 11 and the catalyst layer 15B of the cathode 15 are different if necessary. For example, the catalyst layer 11B may have a chemical structure of M′_(a)M″_(b)N₂ or M′_(c)M″_(d)C_(e), and the catalyst layer 15B may have a chemical structure of M_(x)Ru_(y)N₂ or M_(x)Ru_(y), wherein M is Ni, Co, Fe, Mn, Cr, V, Ti, Cu, or Zn, 0<x<1.3, 0.7<y<2, x+y=2, M_(x)Ru_(y)N₂ is a cubic crystal system or amorphous, and M_(x)Ru_(y) is a cubic crystal system. In this embodiment, the gas-liquid diffusion layer 11A can be a porous metal mesh, and the gas-liquid diffusion layer 11B can be a porous carbon paper to further increase the durability of the membrane electrode assembly in electrolysis. Alternatively, the catalyst layer 11B has a chemical structure of M′_(a)M″_(b)N₂ or M′_(c)M″_(d)C_(e), and the cathode 15 can be a commercially available electrode.

The membrane electrode assembly can be used to generating hydrogen by electrolysis. For example, the membrane electrode assembly can be dipped in alkaline aqueous solution. The alkaline aqueous solution can be an aqueous solution of NaOH, KOH, another suitable alkaline, or a combination thereof. In one embodiment, the alkaline aqueous solution has a pH value of greater than 14 and less than 15. If the pH value of the alkaline aqueous solution is too low, the conductivity of the alkaline aqueous solution will be poor. If the pH value of the alkaline aqueous solution is too high, the viscosity of the alkaline aqueous solution will be too high. The method also applies a voltage to the anode and the cathode to electrolyze the alkaline aqueous solution to generate hydrogen by the cathode and generate oxygen by the anode.

Accordingly, the catalyst of the embodiments meets the requirement of electrolyzing alkaline aqueous solution to generate hydrogen. In OER aspect, the catalyst in the embodiments may overcome the poor catalytic effect, poor conductivity, low corrosion resistance, low anti-oxidation ability, and other problems of conventional catalysts. The catalyst should have a high conductivity and high electrochemical activity of OER. In view of the diffusion in the catalyst of the embodiments, the grain boundary diffusion coefficient is greatly larger than the body diffusion coefficient at a low temperature. Because the impurity atoms added into the catalyst may fill the grain boundaries, which may block the diffusion of atoms via the grain boundaries for improving the catalyst performance. The fast diffusion path of the catalyst (e.g. grain boundaries) can be filled by some material, thereby preventing the adjacent material atoms from diffusion via the grain boundaries or other defects. The diffusion of the atoms via grain boundaries is greatly reduced by introducing nitrogen atoms or carbon atoms into the seams of grain boundaries. Accordingly, the nitrogen atom and carbon atom can increase the anti-oxidation ability and stability of the catalyst material. Because the nitride and the carbide has excellent conductivity and simultaneously meet the requirements of activity and cost, the nitride or carbide of M″ (has an activity similar to Pt) can be combined with M′ to obtain the catalyst with high conductivity and electrochemical activity.

Below, exemplary embodiments will be described in detail with reference to accompanying drawings so as to be easily realized by a person having ordinary knowledge in the art. The inventive concept may be embodied in various forms without being limited to the exemplary embodiments set forth herein. Descriptions of well-known parts are omitted for clarity, and like reference numerals refer to like elements throughout.

EXAMPLES Preparation Example 1

Pt catalyst was deposited on a glass carbon electrode (5 mm OD×4 mm H) by a reactive magnetron sputter. A Pt target was put into the sputter to be applied a power. Nitrogen with a flow rate of 20 sccm was introduced into the sputter, and the pressure in the sputter was 30 mTorr. The Pt target was bombarded by argon ions to perform the sputtering at room temperature for 5 minutes to 6 minutes, thereby forming the Pt catalyst with a thickness of about 100 nm on the glass carbon electrode. The loading amount of the catalyst was 0.042 mg.

Preparation Example 2

Ni_(x)Ru_(y) catalysts of different element ratios were respectively deposited on glass carbon electrodes (5 mm OD×4 mm H) by the reactive magnetron sputter. A Ni target and a Ru target were put into the sputter, and powers applied to the Ni target (10 W to 200 W) and the Ru target (10 W to 200 W) were adjusted. Nitrogen with a flow rate of 20 sccm was introduced into the sputter, and the pressure in the sputter was 20 mTorr. The Ni target and the Ru target were bombarded by argon ions to perform the reactive sputtering at room temperature for 5 minutes to 6 minutes, thereby respectively forming the Ni_(x)Ru_(y) catalysts with a thickness of about 100 nm on the glass carbon electrodes. The loading amount of the catalyst was 0.024 mg. The Ni_(x)Ru_(y) catalysts had x of about 0.065 to 0.85 and y of about 1.935 to 1.15, which were determined by EDS. The Ni_(x)Ru_(y) catalysts had surface morphology of granular, which were determined by SEM. The Ni_(x)Ru_(y) catalysts were cubic crystal system, which were determined by X-ray diffraction. In addition, only the Ru target was put into the sputter to form a Ru catalyst film with a thickness of 100 nm on the glass carbon electrode by the similar conditions, and the catalyst loading amount was 0.024 mg.

Preparation Example 3

Ni_(x)Ru_(y)N₂ catalysts of different element ratios were respectively deposited on glass carbon electrodes (5 mm OD×4 mm H) by the reactive magnetron sputter. A Ni target and a Ru target were put into the sputter, and powers applied to the Ni target (10 W to 200 W) and the Ru target (10 W to 200 W) were adjusted. Nitrogen and argon with a total flow rate of 20 sccm (e.g. nitrogen:(nitrogen+argon)=50:100) were introduced into the sputter, and the pressure in the sputter was 20 mTorr. The Ni target and the Ru target were bombarded by argon ions to perform the reactive sputtering at room temperature for 5 minutes to 6 minutes, thereby respectively forming the Ni_(x)Ru_(y)N₂ catalysts with a thickness of about 100 nm on the glass carbon electrodes. The loading amount of the catalyst was 0.024 mg. The Ni_(x)Ru_(y)N₂ catalysts had x of about 0.069 to 1.086 and y of about 1.931 to 0.914, which were determined by EDS. The Ni_(x)Ru_(y)N₂ catalysts had surface morphology of tetrahedron or pyramidal, which were determined by SEM. The Ni_(x)Ru_(y)N₂ catalysts were cubic crystal system, which were determined by X-ray diffraction. In addition, only the Ru target was put into the sputter to form a Ru₂N₂ catalyst film with a thickness of 100 nm on the glass carbon electrode by the similar conditions, and the catalyst loading amount was 0.024 mg.

Example 1

The OER electrochemical activities of the Pt, Ru, Ru₂N₂, Ni_(x)Ru_(y), and Ni_(x)Ru_(y)N₂ catalysts were tested as below. In 0.1M KOH solution, the glass carbon electrode with the Pt, Ru, Ru₂N₂, Ni_(x)Ru_(y), or Ni_(x)Ru_(y)N₂ catalyst formed thereon served as a working electrode. Hg/HgO served as a reference electrode, and platinum served as an auxiliary electrode. The scan voltage ranged from −0.8V to 1V, the scan rate was 50 mV/s, and the number of scans was 10. Subsequently, the CV measurement of the OER was performed, in which the scan voltage ranged from −0.8V to 0.1V, the scan rate was 10 mV/s, and the number of scans was 5. The OER results are shown in FIG. 2 (e.g. Ru and Ni_(x)Ru_(y)) and FIG. 3 (Ru₂N₂ and Ni_(x)Ru_(y)N₂). The horizontal axis in FIGS. 2 and 3 is potential (V) of reversible hydrogen electrode (RHE), and the vertical axis in FIGS. 2 and 3 is current density (J, mA/cm²). As shown in FIG. 2, the pure Ru catalyst was free of the OER activity, and the activities of the Ru catalysts doped with appropriate amounts of Ni were obviously enhanced. As shown in FIG. 3, the activity of the Ru₂N₂ catalyst was greatly higher than the activity of the Ru catalyst, and the activities of the Ru₂N₂ catalysts doped with appropriate amounts of Ni (e.g. Ni_(x)Ru_(y)N₂ catalysts) were greatly enhanced. For example, the Ni_(x)Ru_(y)N₂ with x of 0.4 to 1.1 could have a better performance. A comparison of some catalysts is shown in Table 1:

TABLE 1 Initial potential (V) for electrolysis of Best current density water (current (mA/cm²) at the RHE density was set to OER comparison potential of 1.65 V 0.5 mA/cm²) Pt film ~10 1.48-1.5  Ni_(0.29)Ru_(1.71) ~15  1.4-1.55 Ni_(0.46)Ru_(1.53)N₂ ~65 1.4-1.5

As shown in Table 1, the current densities of the Ni_(0.29)Ru_(1.71) and Ni_(0.46)Ru_(1.53)N₂ catalysts were higher than the current density of the Pt film catalyst in OER. However, the Ni_(x)Ru_(y) was free of the anti-oxidation ability, it should be improper to be applied in OER. In other words, the Ni_(0.46)Ru_(1.53)N₂ catalyst was more suitable than the Pt film catalyst in the application of OER.

Example 2

The HER electrochemical activities of the Pt, Ru, Ni_(x)Ru_(y), and Ni_(x)Ru_(y)N₂ catalysts were tested as below. In 0.1M KOH solution, the glass carbon electrode with the Pt, Ru, Ru₂N₂, Ni_(x)Ru_(y), or Ni_(x)Ru_(y)N₂ catalyst formed thereon served as a working electrode. Hg/HgO served as a reference electrode, and platinum served as an auxiliary electrode. In measurements of the HER, the working electrode was rotated at 1600 rpm, the scan voltage ranged from 0 to 1V, the scan rate was 10 mV/s, and the number of scans was 3. The HER results are shown in FIG. 4 (e.g. Ru and Ni_(x)Ru_(y)) and FIG. 5 (Ru and Ni_(x)Ru_(y)N₂). The horizontal axis in FIGS. 2 and 3 is potential (V) of reversible hydrogen electrode (RHE), and the vertical axis in FIGS. 2 and 3 is current density (J, mA/cm²). As shown in FIG. 4, the activities of the Ru catalysts doped with Ni (e.g. Ni_(x)Ru_(y)) were obviously higher than the activity of the Ru catalyst. A comparison of some catalysts is shown in Table 2:

TABLE 2 Best current density (mA/cm²) HER comparison at the RHE potential of 0.3 V Pt film 14 Ru film ~10 Ni_(0.06)Ru_(1.93) 55 Ni_(1.2)Ru_(0.8)N₂ 19.5

As shown above, the current densities of the Ni_(0.06)Ru_(1.93) and Ni_(1.2)Ru_(0.8)N₂ catalysts were higher than the current density of the Pt film catalyst in HER. In other words, the Ni_(0.06)Ru_(1.93) and Ni_(1.2)Ru_(0.8)N₂ catalyst was more suitable than the Pt film catalyst in the application of HER.

Preparation Example 4

Mn_(x)Ru_(y)N₂ catalysts of different element ratios were respectively deposited on glass carbon electrodes (5 mm OD×4 mm H) by the reactive magnetron sputter. An Mn target and a Ru target were put into the sputter, and powers applied to the Mn target (10 W to 200 W) and the Ru target (10 W to 200 W) were adjusted. Nitrogen and argon with a total flow rate of 20 sccm (e.g. nitrogen:(nitrogen+argon)=50:100) were introduced into the sputter, and the pressure in the sputter was 20 mTorr. The Mn target and the Ru target were bombarded by argon ions to perform the reactive sputtering at room temperature for 5 minutes to 6 minutes, thereby respectively forming the Mn_(x)Ru_(y)N₂ catalysts with a thickness of about 100 nm on the glass carbon electrodes. The loading amount of the catalyst was 0.024 mg. The Mn_(x)Ru_(y)N₂ catalysts had x of about 0.01 to 0.8 and y of about 1.2 to 1.99, which were determined by EDS.

Example 3

The OER electrochemical activities of the Mn_(x)Ru_(y)N₂ catalysts were tested as below. In 0.1M KOH solution, the glass carbon electrode with the Mn_(x)Ru_(y)N₂ catalyst formed thereon served as a working electrode. Hg/HgO served as a reference electrode, and platinum served as an auxiliary electrode. The working electrode was rotated at 1600 rpm. The scan voltage ranged from −0.8V to 1V, the scan rate was 50 mV/s, and the number of scans was 10. Subsequently, the CV measurement of the OER was performed, in which the scan voltage ranged from −0.8 V to 0.1 V, the scan rate was 10 mV/s, and the number of scans was 5. The OER results are shown in FIG. 6 (Ni₂N₂ and Mn_(x)Ru_(y)N₂). The horizontal axis in FIG. 6 is potential (V) of reversible hydrogen electrode (RHE), and the vertical axis in FIG. 6 is current density (J, mA/cm²). As shown in FIG. 6, the activities of the Ru₂N₂ catalysts doped with appropriate amounts of Mn (e.g. Mn_(x)Ru_(y)N₂ catalysts) were greatly enhanced. For example, the Mn_(x)Ru_(y)N₂ with x of 0.3 to 0.7 could have a better performance. A comparison of some catalysts is shown in Table 3:

TABLE 3 Initial potential (V) for electrolysis of Best current density water (current (mA/cm²) at the RHE density was set to OER comparison potential of 1.65 V 0.5 mA/cm²) Pt film ~10 1.48-1.5 Mn_(0.323)Ru_(1.677)N₂ 13  1.5-1.55

As shown in Table 3, the current density of the Mn_(0.323)Ru_(1.677)N₂ catalyst was higher than the current density of the Pt film catalyst in OER. In other words, the Mn_(0.323)Ru_(1.677)N₂ catalyst was more suitable than the Pt film catalyst in the application of OER.

Example 4

The HER electrochemical activities of the Mn_(x)Ru_(y)N₂ catalysts were tested as below. In 0.1 M KOH solution, the glass carbon electrode with the Mn_(x)Ru_(y)N₂ catalyst formed thereon served as a working electrode. Hg/HgO served as a reference electrode, and platinum served as an auxiliary electrode. In measurements of the HER, the working electrode was rotated at 1600 rpm, the scan voltage ranged from 0 to 1V, the scan rate was 10 mV/s, and the number of scans was 3. The HER results are shown in FIG. 7. The horizontal axis in FIG. 7 is potential (V) of reversible hydrogen electrode (RHE), and the vertical axis in FIG. 7 is current density (J, mA/cm²). A comparison of some catalysts is shown in Table 4:

TABLE 4 Best current density (mA/cm²) HER comparison at the RHE potential of 0.3 V Pt film 14 Ru film ~10 Mn_(0.079)Ru_(1.92)N₂ 28

As shown above, the current density of the Mn_(0.079)Ru_(1.92)N₂ catalyst was higher than the current density of the Pt film catalyst in HER. In other words, the Mn_(0.079)Ru_(1.92)N₂ catalyst was more suitable than the Pt film catalyst in the application of HER.

Preparation Example 5

Ni_(a)Nb_(b)N₂ catalysts of different element ratios were respectively deposited on glass carbon electrodes (5 mm OD×4 mm H) by the reactive magnetron sputter. A Ni target and a Nb target were put into the sputter, and powers applied to the Ni target (10 W to 200 W) and the Nb target (10 W to 200 W) were adjusted. Nitrogen and argon with a total flow rate of 10 sccm (e.g. nitrogen:(nitrogen+argon)=50:100) were introduced into the sputter, and the pressure in the sputter was 5 mTorr. The Ni target and the Nb target were bombarded by argon ions to perform the reactive sputtering at room temperature for 5 minutes to 6 minutes, thereby respectively forming the Ni_(a)Nb_(b)N₂ catalysts with a thickness of about 100 nm on the glass carbon electrodes. The loading amount of the catalyst was 0.017 mg. The Ni_(a)Nb_(b)N₂ catalysts had a of about 0.3128 to 1.5082 and y of about 0.5095 to 1.6872, which were determined by EDS. The Ni_(a)Nb_(b)N₂ catalysts were cubic crystal system, which were determined by XRD.

Preparation Example 6

Ni_(c)Nb_(d)C_(e) catalysts of different element ratios were respectively deposited on glass carbon electrodes (5 mm OD×4 mm H) by the reactive magnetron sputter. A Ni target, a Nb target, and a carbon target were put into the sputter, and powers applied to the Ni target (10 W to 200 W), the Nb target (10 W to 200 W), and the carbon target (10 W to 200 W) were adjusted. Argon with a flow rate of 10 sccm was introduced into the sputter, and the pressure in the sputter was 5 mTorr. The Ni target, the Nb target, and the carbon target were bombarded by argon ions to perform the reactive sputtering at room temperature for 5 minutes to 6 minutes, thereby respectively forming the Ni_(c)Nb_(d)C_(e) catalysts with a thickness of about 100 nm on the glass carbon electrodes. The loading amount of the catalyst was 0.017 mg. The Ni_(c)Nb_(d)C_(e) catalysts had c of about 0.58 to 1.47, d of about 0.53 to 1.42, and e of about 0.92 to 2.47, which were determined by EDS. The Ni_(c)Nb_(d)C_(e) catalysts were cubic crystal system or amorphous, which were determined by XRD. In addition, only the Nb target and the carbon target were put into the sputter to form Nb_(0.6556)C_(1.3444) catalyst film with a thickness of 100 nm on the glass carbon electrode by the similar conditions, and the catalyst loading amount was 0.017 mg.

Preparation Example 7

Ni_(c)Nb_(d)C_(e) catalysts of different element ratios were respectively deposited on glass carbon electrodes (5 mm OD×4 mm H) by the reactive magnetron sputter. A Ni target, a Nb target, and a carbon target were put into the sputter, and powers applied to the Ni target (10 W to 200 W), the Nb target (10 W to 200 W), and the carbon target (10 W to 200 W) were adjusted. Argon with a flow rate of 10 sccm was introduced into the sputter, and the pressure in the sputter was 5 mTorr. The Ni target, the Nb target, and the carbon target were bombarded by argon ions to perform the reactive sputtering at room temperature for 5 minutes to 6 minutes, thereby respectively forming the Ni_(c)Nb_(d)C_(e) catalysts with a thickness of about 100 nm on the glass carbon electrodes. The loading amount of the catalyst was 0.017 mg. The Ni_(c)Nb_(d)C_(e) catalysts had c of about 0.74 to 1.63, d of about 0.37 to 1.26, and e of about 0.38 to 1.30, which were determined by EDS. The Ni_(c)Nb_(d)C_(e) catalysts were cubic crystal system or amorphous, which were determined by XRD.

Example 5

The OER electrochemical activities of the Pt, Ni_(a)Nb_(b)N₂, NicNb_(d)C_(e), and Nb_(0.6556)C_(1.3444) catalysts were tested as below. In 0.1M KOH solution, the glass carbon electrode with the Pt, Ni_(a)Nb_(b)N₂, NicNb_(d)C_(e), or Nb_(0.6556)C_(1.3444) catalyst formed thereon served as a working electrode. Hg/HgO served as a reference electrode, and platinum served as an auxiliary electrode. The working electrode was rotated at 1600 rpm. The scan voltage ranged from −0.8V to 1V, the scan rate was 50 mV/s, and the number of scans was 10. Subsequently, the CV measurement of the OER was performed, in which the scan voltage ranged from −0.8V to 0.1V, the scan rate was 10 mV/s, and the number of scans was 5. The OER results are shown in FIG. 8 (e.g. Ni_(a)Nb_(b)N₂), FIG. 9 (Ni_(c)Nb_(d)C_(e) and Nb_(0.6556)C_(1.3444)), and FIG. 10 (Ni_(c)Nb_(d)C_(e) and Nb_(0.6556)C_(1.3444)). The horizontal axis in FIGS. 8 to 10 is potential (V) of reversible hydrogen electrode (RHE), and the vertical axis in FIGS. 8 to 10 is current density (J, mA/cm²). As shown in FIG. 8, the activities of the Nb₂N₂ catalysts doped with appropriate amounts of Ni (e.g. Ni_(a)Nb_(b)N₂ catalysts) were greatly enhanced. As shown in FIGS. 9 and 10, the activities of the NbC catalysts doped with appropriate amounts of Ni (e.g. Ni_(c)Nb_(d)C_(e) catalysts) were greatly enhanced. A comparison of some catalysts is shown in Table 5:

TABLE 5 Initial potential (V) for electrolysis of Best current density water (current (mA/cm²) at the RHE density was set to OER comparison potential of 1.8 V 0.5 mA/cm²) Pt ~18 1.48-1.5  Ni_(1.5)Nb_(0.5)N₂ ~22 1.5-1.55 Ni_(1.62)Nb_(0.37)C_(0.39) ~28 1.5-1.55

As shown in Table 5, the current densities of the Ni_(1.5)Nb_(0.5)N₂ and Ni_(1.62)Nb_(0.37)C_(0.39) catalysts were higher than the current density of the Pt film catalyst in OER. In other words, the Ni_(1.5)Nb_(0.5)N₂ and Ni_(1.62)Nb_(0.37)C_(0.39) catalysts were more suitable than the Pt film catalyst in the application of OER.

Preparation Example 8

Co_(c)Nb_(d)C_(e) catalysts of different element ratios were respectively deposited on glass carbon electrodes (5 mm OD×4 mm H) by the reactive magnetron sputter. A Co target, a Nb target, and a carbon target were put into the sputter, and powers applied to the Co target (30 W to 100 W), the Nb target (35 W), and the carbon target (100 W) were adjusted. Argon with a flow rate of 10 sccm was introduced into the sputter, and the pressure in the sputter was 5 mTorr. The Co target, the Nb target, and the carbon target were bombarded by argon ions to perform the reactive sputtering at room temperature for 10 minutes to 15 minutes, thereby respectively forming the Co_(c)Nb_(d)C_(e) catalysts with a thickness of about 100 nm on the glass carbon electrodes. The loading amount of the catalyst was 0.017 mg. The Co_(c)Nb_(d)C_(e) catalysts had c of about 0.24 to 1.39, d of about 0.61 to 1.76, and e of about 0.63 to 1.76, which were determined by EDS. The Co_(c)Nb_(d)C_(e) catalysts were cubic crystal system or amorphous, which were determined by XRD.

Example 6

The OER electrochemical activities of the Co_(c)Nb_(d)C_(e) and Nb_(0.6556)C_(1.3444) catalysts were tested as below. In 0.1M KOH solution, the glass carbon electrode with the Co_(c)Nb_(d)C_(e) or Nb_(0.6556)C_(1.3444) catalyst formed thereon served as a working electrode. Hg/HgO served as a reference electrode, and platinum served as an auxiliary electrode. The working electrode was rotated at 1600 rpm. The scan voltage ranged from −0.8V to 1V, the scan rate was 50 mV/s, and the number of scans was 10. Subsequently, the CV measurement of the OER was performed, in which the scan voltage ranged from −0.8V to 0.1V, the scan rate was 10 mV/s, and the number of scans was 5. The OER results are shown in FIGS. 11 to 15 (Co_(c)Nb_(d)C_(e) and Nb_(0.6556)C_(1.3444)). The horizontal axis in FIGS. 11 to 15 is potential (V) of reversible hydrogen electrode (RHE), and the vertical axis in FIGS. 11 to 15 is current density (J, mA/cm²). As shown in FIGS. 11 to 15, the activities of the Nb_(d)C_(e) catalysts doped with appropriate amounts of Co (e.g. Co_(c)Nb_(d)C_(e) catalysts) were greatly enhanced.

Preparation Example 9

Ni_(1.5)Nb_(0.5)N₂ catalyst was deposited on stainless steel mesh (316 stainless steel, 200 mesh, 50 mm×50 mm) by the reactive magnetron sputter. A Ni target and a Nb target were put into the sputter, and powers applied to the Ni target (10 W to 200 W) and the Nb target (10 W to 200 W) were adjusted. Nitrogen and argon with a total flow rate of 10 sccm (e.g. nitrogen:(nitrogen+argon)=50:100) were introduced into the sputter, and the pressure in the sputter was 5 mTorr. The Ni target and the Nb target were bombarded by argon ions to perform the reactive sputtering at room temperature for 8 minutes, thereby forming the Ni_(1.5)Nb_(0.5)N₂ catalysts (determined by EDS) with a thickness of about 300 nm on the stainless steel mesh. The loading amount of the catalyst per area was 0.17 mg/cm². The Ni_(1.5)Nb_(0.5)N₂ catalyst was cubic crystal systems, which was determined by XRD.

Example 7

Commercially available PtC (HISPEC 13100, Johnson Matthey) was coated on a carbon paper H23C8 (Freudenberg) to serve as a cathode of HER, and the loading amount of the cathode catalyst per area was controlled to 1.8 mg/cm². The Ni_(1.5)Nb_(0.5)N₂-stainless steel mesh in Preparation Example 9 served as the anode of OER, and an anionic exchange film X37-50 (commercially available from Dioxide Materials) was interposed between the catalyst layers of the cathode and the anode to obtain a membrane electrode assembly. The membrane electrode assembly was dipped in 2M KOH solution to test its electrochemical activity. The scan voltage ranged from 1.3 V to 2.2 V and the scan rate was 50 mV/s. The curve of current versus voltage of the membrane electrode assembly is shown in FIG. 16. The membrane electrode assembly could generate a current of 10.2 A, and the impedance of the entire test system was 27 mΩ. The decay rate per minute of the membrane electrode assembly was 0.001%.

Preparation Example 10

Ni_(1.62)Nb_(0.37)C_(0.39) catalyst was deposited on stainless steel mesh (316 stainless steel, 200 mesh, 50 mm×50 mm) by the reactive magnetron sputter. A Ni target, a Nb target, and a carbon target were put into the sputter, and powers applied to the Ni target (10 W to 200 W), the Nb target (10 W to 200 W), and the carbon target (10 W to 200 W) were adjusted. Argon with a flow rate of 10 sccm was introduced into the sputter, and the pressure in the sputter was 5 mTorr. The Ni target, the Nb target, and the carbon target were bombarded by argon ions to perform the reactive sputtering at room temperature for 8 minutes, thereby forming the Ni_(1.62)Nb_(0.37)C_(0.39) catalysts (determined by EDS) with a thickness of about 300 nm on the stainless steel mesh. The loading amount of the catalyst per area was 0.17 mg/cm². The Ni_(1.62)Nb_(0.37)C_(0.39) catalyst was cubic crystal systems or amorphous, which was determined by XRD.

Example 8

Commercially available PtC (HISPEC 13100, Johnson Matthey) was coated on a carbon paper H23C8 (Freudenberg) to serve as a cathode of HER, and the loading amount of the cathode catalyst per area was controlled to 1.8 mg/cm². The Ni_(1.62)Nb_(0.37)C_(0.39)-stainless steel mesh in Preparation Example 10 served as the anode of OER, and an anionic exchange film X37-50 (commercially available from Dioxide Materials) was interposed between the catalyst layers of the cathode and the anode to obtain a membrane electrode assembly. The membrane electrode assembly was dipped in 2M KOH solution to test its electrochemical activity. The scan voltage ranged from 1.3 V to 2.2 V and the scan rate was 50 mV/s. The curve of current versus voltage of the membrane electrode assembly is shown in FIG. 17. The membrane electrode assembly could generate a current of 10.2 A, and the impedance of the entire test system was 33 mΩ. The decay rate per minute of the membrane electrode assembly was 0.02%.

Comparative Example 1

Commercially available PtC (HISPEC 13100, Johnson Matthey) was coated on a carbon paper H23C8 (Freudenberg) to serve as a cathode of HER, and the loading amount of the cathode catalyst per area was controlled to 1.8 mg/cm². Commercially available insoluble anode (IrO₂/RuO₂—Ti mesh, Ultrapack Energy Co., Ltd) served as the anode of OER, and an anionic exchange film X37-50 (commercially available from Dioxide Materials) was interposed between the catalyst layers of the cathode and the anode to obtain a membrane electrode assembly. The membrane electrode assembly was dipped in 2M KOH solution to test its electrochemical activity. The scan voltage ranged from 1.3 V to 2.2V and the scan rate was 50 mV/s. The curve of current versus voltage of the membrane electrode assembly is shown in FIG. 18. The membrane electrode assembly could generate a current of 10.6 A, and the impedance of the entire test system was 40 mΩ. The decay rate per minute of the membrane electrode assembly was 0.0087%.

Comparison of the membrane electrode assemblies in Example 7, Example 8, and Comparative Example 1 are shown in Table 6:

TABLE 6 Initial Loading Loading potential amount amount OER Decay (V) for of the of the catalyst rate electrolysis of catalyst catalyst activity per water (current per area per area (A/mg) minute density was set Cathode (mg/cm²) Anode (mg/cm²) at 2 V (%) to 0.5 mA/cm²) Example 7 PtC/H23C8 1.8 Ni_(1.5)Nb_(0.5)N₂- 0.17 2.37 0.001 1.52 stainless steel mesh Example 8 PtC/H23C8 1.8 Ni_(1.62)Nb_(0.37)C_(0.39)- 0.17 2.41 0.02 1.51 stainless steel mesh Comparative PtC/H23C8 1.8 IrO₂/RuO₂-Ti 2 0.23 0.0087 1.52 Example 1 mesh

As shown in Table 6, the activities of the Ni_(1.5)Nb_(0.5)N₂ catalyst and the Ni_(1.62)Nb_(0.37)C_(0.39) catalyst were greatly higher than the activity of the commercially available anode catalyst.

Preparation Example 11

Ni_(0.75)Ru_(1.25)N₂ catalyst was deposited on stainless steel mesh (316 stainless steel, 200 mesh, 50 mm×50 mm) by the reactive magnetron sputter. A Ni target and a Ru target were put into the sputter, and powers were applied to the Ni target (150 W) and the Ru target (100 W). Nitrogen and argon (e.g. nitrogen:(nitrogen+argon)=50:100) were introduced into the sputter, and the pressure in the sputter was 5 mTorr. The Ni target and the Ru target were bombarded by argon ions to perform the reactive sputtering at room temperature for 8 minutes, thereby forming the Ni_(0.75)Ru_(1.25)N₂ catalysts (determined by EDS) with a thickness of about 300 nm on the stainless steel mesh. The loading amount of the catalyst per area was 0.17 mg/cm². The Ni_(0.75)Ru_(1.25)N₂ catalyst had surface morphology of tetrahedron or pyramidal, which were determined by SEM. The Ni_(0.75)Ru_(1.25)N₂ catalyst was cubic crystal systems or amorphous, which was determined by XRD.

Example 9

The Ni_(0.75)Ru_(1.25)N₂-stainless steel mesh in Preparation Example 11 served as the cathode of HER, the Ni_(1.5)Nb_(0.5)N₂-stainless steel mesh in Preparation Example 9 served as the anode of OER, and an anionic exchange film X37-50 (commercially available from Dioxide Materials) was interposed between the catalyst layers of the cathode and the anode to obtain a membrane electrode assembly. The membrane electrode assembly was dipped in 2M KOH solution to test its electrochemical activity. The scan voltage ranged from 1.3V to 2.2V and the scan rate was 50 mV/s. The membrane electrode assembly could generate a current of 10.5 A at 1.87V, and the impedance of the entire test system was 12 mΩ. The decay rate per minute of the membrane electrode assembly was 0.0057%.

Preparation Example 12

Ni_(0.75)Ru_(1.25)N₂ catalyst was deposited on carbon paper (H23C8, Freudenberg, 50 mm×50 mm) by the reactive magnetron sputter. A Ni target and a Ru target were put into the sputter, and powers were applied to the Ni target (150 W) and the Ru target (100 W). Nitrogen and argon (e.g. nitrogen:(nitrogen+argon)=50:100) were introduced into the sputter, and the pressure in the sputter was 5 mTorr. The Ni target and the Ru target were bombarded by argon ions to perform the reactive sputtering at room temperature for 8 minutes, thereby forming the Ni_(0.75)Ru_(1.25)N₂ catalysts (determined by EDS) with a thickness of about 300 nm on the carbon paper H23C8. The loading amount of the catalyst per area was 0.17 mg/cm². The Ni_(0.75)Ru_(1.25)N₂ catalyst had surface morphology of tetrahedron or pyramidal, which were determined by SEM. The Ni_(0.75)Ru_(1.25)N₂ catalyst was cubic crystal systems or amorphous, which was determined by XRD.

Example 10

The Ni_(0.75)Ru_(1.25)N₂-carbon paper in Preparation Example 12 served as the cathode of HER, the Ni_(1.5)Nb_(0.5)N₂-stainless steel mesh in Preparation Example 9 served as the anode of OER, and an anionic exchange film X37-50 (commercially available from Dioxide Materials) was interposed between the catalyst layers of the cathode and the anode to obtain a membrane electrode assembly. The membrane electrode assembly was dipped in 2M KOH solution to test its electrochemical activity. The scan voltage ranged from 1.3V to 2.2V and the scan rate was 50 mV/s. The curve of current versus voltage of the membrane electrode assembly is shown in FIG. 19. The membrane electrode assembly could generate a current of 10.5 A at 1.96V, and the impedance of the entire test system was 17 mΩ. The decay rate per minute of the membrane electrode assembly was 0.000035%. The potential of the membrane electrode assembly was controlled at 2V to continuously operate 48 hours, and its current was stable as shown in FIG. 20. In other words, the Ni_(0.75)Ru_(1.25)N₂-carbon paper could withstand the chemically reduction, the Ni_(1.5)Nb_(0.5)N₂-stainless steel mesh could withstand the oxidation, and the Ni_(0.75)Ru_(1.25)N₂-carbon paper and the Ni_(1.5)Nb_(0.5)N₂-stainless steel mesh could resist the alkaline corrosion.

Comparison of the membrane electrode assemblies in Example 7, Example 9, and Example 10 are shown in Table 7:

TABLE 7 Loading Loading Initial potential amount amount OER Decay (V) for of the of the catalyst rate electrolysis of catalyst catalyst activity per water (current per area per area (A/mg) minute density was set Cathode (mg/cm²) Anode (mg/cm²) at 2 V (%) to 0.5 mA/cm²) Example 9 Ni_(0.75)Ru_(1.25)N₂- 0.17 Ni_(1.5)Nb_(0.5)N₂- 0.17 2.47 0.0057 1.53 staineless stainless steel steel mesh mesh Example 10 Ni_(0.75)Ru_(1.25)N₂ 0.17 Ni_(1.5)Nb_(0.5)N₂- 0.17 2.47 0.000035 1.50 —H23C8 stainless steel mesh Example7 PtC/H23C8 1.8 Ni_(1.5)Nb_(0.5)N₂- 0.17 0.23 0.07 1.50 stainless steel mesh

As shown in Table 7, the Ni_(0.75)Ru_(1.25)N₂ catalyst serving as the catalyst layer of the cathode could greatly enhance the catalyst activity. In addition, the Ni_(0.75)Ru_(1.25)N₂ catalyst formed on the carbon paper could further improve the durability of the membrane electrode assembly.

It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed methods and materials. It is intended that the specification and examples be considered as exemplary only, with the true scope of the disclosure being indicated by the following claims and their equivalents. 

What is claimed is:
 1. A membrane electrode assembly, comprising: an anode having a first catalyst layer on a first gas-liquid diffusion layer; a cathode having a second catalyst layer on a second gas-liquid diffusion layer; and an anionic exchange membrane between the first catalyst layer of the anode and the second catalyst layer of the cathode, wherein the first catalyst layer has a chemical structure of M′_(a)M″_(b)N₂ or M′_(c)M″_(d)C_(e), wherein M′ is Ni, Co, Fe, Mn, Cr, V, Ti, Cu, or Zn, M″ is Nb, Ta, or a combination thereof, 0.7≤a≤1.7, 0.3≤b≤1.3, a+b=2, 0.24≤c≤1.7, 0.3≤d≤1.76, and 0.38≤e≤3.61, wherein M′_(a)M″_(b)N₂ is a cubic crystal system and M′_(c)M″_(d)C_(e) is a cubic crystal system or amorphous.
 2. The membrane electrode assembly as claimed in claim 1, dipped in an alkaline aqueous solution.
 3. The membrane electrode assembly as claimed in claim 1, wherein the first layer has a chemical structure of Ni_(a)Nb_(b)N₂, 0.7≤a≤1.51, and 0.49≤b≤1.30.
 4. The membrane electrode assembly as claimed in claim 1, wherein the first layer has a chemical structure of Ni_(c)Nb_(d)C_(e), 0.90≤c≤1.47, 0.53≤d≤1.10, and 0.9≤e≤1.9.
 5. The membrane electrode assembly as claimed in claim 1, wherein the first layer has a chemical structure of Ni_(c)Nb_(d)C_(e), 0.74≤c≤1.63, 0.37≤d≤1.26, and 0.38≤e≤1.30.
 6. The membrane electrode assembly as claimed in claim 1, wherein the first layer has a chemical structure of Co_(c)Nb_(d)C_(e), 0.24≤c≤1.39, 0.61≤d≤1.76, and 0.63≤e≤3.61.
 7. The membrane electrode assembly as claimed in claim 1, wherein the second catalyst layer has a chemical structure of M_(x)Ru_(y)N₂ or M_(x)Ru_(y), wherein M is Ni, Co, Fe, Mn, Cr, V, Ti, Cu, or Zn, 0<x<1.3, 0.7<y<2, x+y=2, M_(x)Ru_(y)N₂ is a cubic crystal system or amorphous, and M_(x)Ru_(y) is a cubic crystal system.
 8. The membrane electrode assembly as claimed in claim 1, wherein each of the first gas-liquid diffusion layer and the second gas-liquid diffusion layer respectively comprises a porous conductive layer.
 9. The membrane electrode assembly as claimed in claim 1, wherein the first gas-liquid diffusion layer is a metal mesh, and the second gas-liquid diffusion layer is another metal mesh or a carbon paper.
 10. The membrane electrode assembly as claimed in claim 8, wherein the first gas-liquid diffusion layer has a pore size of 40 micrometers to 150 micrometers, and the second gas-liquid diffusion layer has a pore size of 0.5 micrometers to 5 micrometers.
 11. A method for hydrogen evolution by electrolysis, comprising: dipping a membrane electrode assembly in an alkaline aqueous solution, wherein the membrane electrode assembly comprises: an anode having a first catalyst layer on a first gas-liquid diffusion layer; a cathode having a second catalyst layer on a second gas-liquid diffusion layer; and an anionic exchange membrane between the first catalyst layer of the anode and the second catalyst layer of the cathode, wherein the first catalyst layer has a chemical structure of M′_(a)M″_(b)N₂ or M′_(c)M″_(d)C_(e), wherein M′ is Ni, Co, Fe, Mn, Cr, V, Ti, Cu, or Zn, M″ is Nb, Ta, or a combination thereof, 0.7≤a≤1.7, 0.3≤b≤1.3, a+b=2, 0.24≤c≤1.7, 0.3≤d≤1.76, and 0.38≤e≤3.61, wherein M′_(a)M″_(b)N₂ is a cubic crystal system and M′_(c)M″_(d)C_(e) is a cubic crystal system or amorphous; and applying a potential to the anode and the cathode to electrolyze the alkaline aqueous solution for generating hydrogen by the cathode and generating oxygen by the anode.
 12. The method as claimed in claim 11, wherein the second catalyst layer has a chemical structure of M_(x)Ru_(y)N₂ or M_(x)Ru_(y), wherein M is Ni, Co, Fe, Mn, Cr, V, Ti, Cu, or Zn, 0<x<1.3, 0.7<y<2, x+y=2, M_(x)Ru_(y)N₂ is a cubic crystal system or amorphous, and M_(x)Ru_(y) is a cubic crystal system.
 13. The method as claimed in claim 11, wherein each of the first gas-liquid diffusion layer and the second gas-liquid diffusion layer comprises a porous conductive layer.
 14. The method as claimed in claim 11, wherein the first gas-liquid diffusion layer is a metal mesh, and the second gas-liquid diffusion layer is another metal mesh or carbon paper.
 15. The method as claimed in claim 11, wherein the first gas-liquid diffusion layer has a pore size of 40 micrometers to 150 micrometers, and the second gas-liquid diffusion layer has a pore size of 0.5 micrometers to 5 micrometers. 